From what I've seen he's not a hedge fund manager, but a more traditional investment manager. There's a good section on him in the book "Value Investing" by B. Greenwald if you're interested.
Yes, he's concentrated and deep value, but what's even more important (for us) is that he is LOW TURNOVER. He holds positions for at least 3 years on average. That dries up supply of shares and more than offsets the impact of any Yorktown distributions.
This is 8-9% of Greenberg's holdings and something like 15% of XTXI. This is a pretty bullish signal (more or less than insider buying, not sure, but certainly good news) and should bring XTXI some more looks.